Brazing is a process for joining metal parts with the help of brazing filler metal and heating. The melting temperature of the brazing filler metal must be below the melting temperature of the base material but above 450° C. If the brazing filler metal has a braze temperature below 450° C. the joining process is called soldering. The most commonly used brazing filler metals for brazing stainless steels are based on copper or nickel. Copper based brazing filler metals are preferred when considering cost advantages while nickel based brazing filler metals are needed in high corrosion and high strength applications. Copper based brazing filler metals are for example often used for brazing of heat exchangers for district heating and for tap water installations.
Nickel based brazing filler metals with high chromium content are used for their high corrosion resistance in applications exposed to corrosive environments. Nickel based brazing filler metals may also be used in high service temperature applications and/or when high strength is required in the application. A typical application exposed to both corrosive environment and high service temperature is the exhaust gas recirculation (EGR) cooler in automotive diesel engines. Brazing filler metals for these applications must have certain properties to be suitable to use such as; corrosion resistance, resistance to high temperature oxidation, good wetting of the base material, without causing embrittlement of the base material during brazing.